1. Field of the Invention
The present invention relates to an improved impact wrench structure, and more particularly to a novel internal structure for an impact wrench having two counterpositioned hammers fixed to a drive wheel and an auxiliary wheel. A spring is engaged to the flyweight side of the brake hammer for restricting the action of the brake hammer. When rotation of the drive wheel rotated by a driving motor reaches to a certain speed, the flyweight side of the brake hammer bounds outwards due to a centrifugal force produced by rotation of the brake hammer itself At this moment the knocking side of the brake hammer drops downward, impacting a reception block of the transmission shaft and engages with it and transmits power to the transmission shaft. The design of the two hammers and incorporated with spring of the present invention contributes to make the impact wrench more practical in application and convenient in assembling and production compared to a conventional one.
2. Description of the Prior Art
The impact wrench available in the market are quite similar in their shapes and functions, but each has its own feature so far as the internal structure is concerned. One of the cases is an utility model under the R.O.C. patent "Spare Tire Installation and Removal Tool" (application Ser. No. 75,207,418), published in R.O.C. Patent Gazette dated Jan. 1, 1987. The internal structure of this utility model is very complicated, it has dozens of components, some of which are intricate in shape, thus causing much inconvenience to the assembling and production.
Another prior art is the utility model "Multipurpose Screw Tightening and Loosening Tool (application Ser. No. 7,821,007) published by the R.O.C. patent Gazette on Mar. 1, 1990. As an improvement of the above-mentioned utility model its structure remains substantially unchanged, the only difference lies on the clutch. The former has a trigger together with a Y-shaped weight board to separate a movable pin from a driving brake element which consequently engaging with a driven brake for transmitting power, while the latter, on the other hand, has a "rapid throwing plate" incorporated with a brake hammer so that when a rotating body reaches a certain rotating speed, "the rapid throwing plate" is expanded outwards by a centrifugal force to separate the movable pin from the brake hammer for transmitting power by engaging the brake hammer with the protruding tooth at the periphery of the brake element. The former is operating mechanically, while the latter makes use of a centrifugal force. Both of them have their own features, but at the same time a weak point in common: they consist of numerous parts and components so that their assembly is time and labor consuming resulting in a high production cost. Moreover, the shapes of some of the components are so complicated that they are difficult to assemble and produce, leading to the obvious shortcoming in terms of the costs and the time spent on assembling.
Furthermore, the impact wrench of the prior art is driven by a motor directly, which requires a higher torque and thus a motor of higher power rating is required, which in turn adds an extra weight to the impact wrench, causing increase of production cost and inconvenience to users as well.